The present invention relates to a method and apparatus for quenching heated bulk materials, especially coke. The quenching liquid flows from the top of the bulk material downwardly through the bulk material, whereby the material is confined against the atmosphere. The vapor generated from the quenching liquid flows in parallel with the quenching liquid downwardly through the material.
It is desirable to produce a substantially dry coke. With this aim in mind, devices have been suggested heretofore, for performing a quenching method. Such devices comprise a mobile quenching car including a cover which closes off the coke from the atmosphere. These quenching cars have a bottom which is slanted against the horizontal and which is provided with vapor exit openings. Thus, the vapor generated during the quenching is forced to flow through the hot or burning coke in parallel flow with the quenching liquid. Due to the slanted bottom of the quenching car, the coke in the quenching car forms a layer which has a depth varying with the width of the car. Thus, the quenching liquid and the resulting vapor flowing in the same direction through the coke must flow through said differing depths.
All the prior art devices require a slanted bottom in the quenching car in order to provide a flow-off for the excess quenching liquid. Thus, the non-uniform depth of the bulk material over the width of the car could not be avoided. Due to the non-uniform depth of the bulk material, it has not been possible heretofore to achieve a uniform quenching. Thus, it has been suggested to adapt the quantity of the quenching liquid to the depth of the bulk material. In other words, it is known in the art to supply more quenching liquid over the deeper portion of the bulk material and to reduce the quantity of the quenching liquid toward the less deeper portion of the bulk material. However, even with this approach a uniform quenching has not been achieved. The distribution of the quenching liquid over a given surface in response to the depth of the bulk material resting on such surface involves substantial costs. However, even if one disregards such costs, a uniform quenching cannot be accomplished because the vapor tends to flow along the path of the least resistance. As a result, quite different flow conditions may exist from point to point over the surface on which the bulk material rests.
It becomes understandable that prior art quenching devices of the type described above have found hardly any practical acceptance if one takes into account the non-uniform quenching resulting from the tilted bottom surface of the quenching car and if one takes into account the further phenomenon which is also known as the Leidenfrost phenomenon. According to this phenomenon, water is repelled from a hot surface, because a vapor skin is formed around a water droplet. As a result, the droplets tend to run down along the slope of the bulk material without effectively participating in the quenching process. Further, in the second half of the quenching phase the generated vapor tends to flow upwardly in a counter-current relative to the down-flowing quenching water. The counter-current vapor flow tends to impede the penetration of the quenching liquid into the bulk material. As a matter of fact, the super-heated vapor rising out of the bulk material absorbs a portion of the water until the vapor becomes saturated. This water is thus removed from participating in the quenching process. For these reasons it is apparent that prior art quenching devices leave room for improvement.
Another drawback of prior art devices is seen in that it is not possible to produce a quenched bulk material having a uniformly low moisture content. Achieving such a low moisture content is not possible, because the lower portions of the bulk material must take up or absorb the excess quenching liquid which becomes available toward the end of the quenching process. It is not possible to avoid such excess of quenching liquid because the liquid is required for a complete quenching of the upper portions of the bulk material. Furthermore, it has not been possible in connection with the use of prior art quenching devices to achieve a uniform vapor temperature throughout the body of the bulk material, because the quenching had to be continued until the vapor temperature is below 400.degree.C throughout the body of the bulk material in order to avoid partial self-ignitions in the bulk material. As a result, the lower layers or portions of the bulk material used to contain at the end of the quenching process a substantially higher moisture content than the upper layers or portions of the bulk material.
According to another prior art process, it is suggested to avoid the finely distributed spraying of the quenching liquid over the coke and to employ instead compact flows of quenching liquid which are forced into the coke bed under pressure. The purpose of this type of quenching is to assure that the quenching liquid rapidly penetrates the higher portions of the bulk material. Further, just as in the above described prior art method, the liquid flows along the tilted bottom of the quenching car, whereby a partial evaporation takes place continuously and the evaporating vapor is supplied to the bulk material above the bottom of the car for cooling the bulk material. This method has the same disadvantages as the above described method, which results from the slanted arrangement of the bulk material. In addition, a very substantial proportion of the available heat of the coke is removed by the portion of the quenching liquid which does not vaporize. This apparently also contributes to the final moisture content of the resulting coke product.